You're making a lot of assumptions, not least of which is that "noble" is the only word linking material wealth and intrinsic goodness. See also "fortune", "blessing", "worth", "value", "credit". Consider also the opposite, like "destitution" (material or moral).

To be clear, I am saying that the link these words connote is wrong, and that it's indeed logical to expect a wealthy person to be selfish. I'm just saying that something drove our culture to forego that logic and make the erroneous link described, and it's written in our language. I can't tell you where that link comes from.